Concrete structures (e.g., walls, ceilings, floors, beams, columns, etc.) are constructed using a formwork, which is erected for the purpose of allowing wet concrete to be retained and shaped into a desired shape and form. Once the concrete has set, the formwork is removed to expose the finished concrete structure. However, the placement and/or configuration of the formwork may create seams between adjoining sections of finished concrete. The seams protrude outward from the surface of the concrete structure and may extend approximately linearly along substantially an entire length of a joint between the adjoining sections. These seams may range in height between approximately one-eighth of an inch (0.3 cm) and approximately one-half inch (1.2 cm). Additionally, the height of the seam may vary along its length.
Due to various functional and/or aesthetic reasons, smoothing these seams, and other surface imperfections, may be needed. For example, seams may be ground substantially flush with a surrounding surface of the concrete structure to give the concrete a better surface finish. Surface finishing is often achieved by a dry grinding operation, in which grinding is performed without supplying water or some other liquid to the concrete surface and/or the tool. Typically, the grinding operation is performed manually with the use of a hand-held grinder tool, commonly referred to as an angle grinder or disc grinder, in which an abrasive disc of the grinder tool is pressed (e.g., at an angle or flat) against the seam and moved along the length of the seam. However, dry grinding generates large amounts of dust having a significant content of respirable size particles of silica (crystalline silica).
Breathing crystalline silica dust can cause silicosis, which in severe cases can be disabling or fatal. Moreover, crystalline silica has been classified as a human lung carcinogen. Due to the serious health hazards posed to workers by silica exposure, the Occupational Safety and Health Administration (OSHA) has an established the Permissible Exposure Limit (PEL), which limits the maximum amount of crystalline silica to which workers may be exposed during an 8-hour work shift to 50 micrograms per cubic meter of air. This new standard demonstrates a significant reduction in allowable silica exposure and requires measurement of the amount of silica exposure each day.
In addition to the PEL, other OSHA standards require operators performing tasks in which there is a risk of silica exposure to wear personal protective equipment (e.g., a respirator mask, gloves, safety glasses, hearing protection, etc.). Despite these precautions, during a concrete grinding operation, the operator may be subjected to various safety hazards including injury caused by projectiles (e.g., pieces of a shattered abrasive disc or shards of concrete), concentrated plums of silica dust, repetitive motion disorders, hearing loss and the like.
Accordingly, those skilled in the art continue with research and development efforts in the field of surface finishing concrete structures.